// Built by perplexity.ai
function maskPhoneNumber(input) {
  input.addEventListener("input", function (e) {
    var x = e.target.value
      .replace(/\D/g, "")
      .match(/(\d{0,3})(\d{0,3})(\d{0,4})/);
    e.target.value = !x[2]
      ? x[1]
      : "(" + x[1] + ") " + x[2] + (x[3] ? "-" + x[3] : "");
  });
}

// Usage
var phoneInput = document.getElementById("phone");
maskPhoneNumber(phoneInput);